This is data collected for a quasi-experimental nurse-led intervention trial based on a convenience sample of three nursing homes. It was collected in the Swiss Canton of Zurich and Thurgau and serves to examine the effects on dementia patients, the healthcare institution, and the qualification level of the healthcare workers using an event analysis and a multilevel analysis. Healthcare workers have been individually trained on how to assess, intervene and evaluate acute and chronic pain with BESD and/or VAS. There are three data-monitoring cycles (T0, T1, T2) and two intervention cycles (I1, I2) with a total study duration of 425 days. The raw data has been cryptographically anonymized using an SSL stream and further de-identification techniques. Also see: 10.1186/s12904-017-0200-5